Develop Reference

Sending java objects as bytes over a http request: is BASE64 necessary?

I have a Java object that is serializable. I need to let another Java webapp do something with this object. I'm currently using this setup to transfer the object:
Use a ByteArrayOutputStream baos
Put the baos in an ObjectOutputStream oos
Write the object using the oos, and get the byte[] from the baos
Use a Base64 encoder to encode the byte[] to another byte[]
send the bytes using a httpurlconnection (POST method)
at the receiving end, I do steps 1 to 4 backwards to get my object back.
This works! However, I'm not sure what step 4, the BASE64 encoding is really doing here. Can't I just send the plain bytes in request's body? What are advantages / safety measures that I get with using the Base64 encoding/decoding?
Here's the relevant code snippet described in step 1-4 I found in this other question.
/** Read the object from Base64 string. */
private static Object fromString( String s ) throws IOException, ClassNotFoundException {
byte [] data = Base64.getDecoder().decode( s );
ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream( data ) );
Object o = ois.readObject();
ois.close();
return o;
}
/** Write the object to a Base64 string. */
private static String toString( Serializable o ) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream( baos );
oos.writeObject( o );
oos.close();
return Base64.getEncoder().encodeToString(baos.toByteArray());
}
}

The purpose of Base64 is to convert a byte array into a human readable (and universally compatible) format.
Because the underlying stream sends data via bytes, and there is no risk of losing data (eg printing to console a control character is not copy/pasteable), there is no point in converting the bytes to Base64. You get no benefits except for possible future compatibility if you change your network protocol to something else that suffers from being unable to transmit non-printable chars.

Invalid stream header 434B0005 from client to server

I've serialized some objects so I can convert them to byte arrays for a TCP packet. When I send the objects from the server program to the client program, there are no issues and it works fine. However, even though the code between the server and client is identical, when I try to send objects from the client to the server I get an invalid header.
Here are the objects I'm serializing:
public static byte[] serialize(Hand c) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(c);
return baos.toByteArray();
}
public static Hand deserialize(byte[] bytes) throws IOException, ClassNotFoundException
{
ByteArrayInputStream b = new ByteArrayInputStream(bytes);
ObjectInputStream o = new ObjectInputStream(b);
return (Hand) o.readObject();
}
and
public static byte[] serialize(Card c) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(c);
return baos.toByteArray();
}
public static Card deserialize(byte[] bytes) throws IOException, ClassNotFoundException
{
ByteArrayInputStream b = new ByteArrayInputStream(bytes);
ObjectInputStream o = new ObjectInputStream(b);
return (Card) o.readObject();
}
Those are both taken from the Server program, but the code for the serialization is identical between the server and the client; I important the Card class and the Hand class from the Server to the Client precisely to make sure errors like this wouldn't occur.
The server can convert a Card or a Hand to a byte[] and write it over a DataOutputStream to the client, and the client can receive the Card or Hand through a DataInputStream, deserialize it, and read it with no problem. When I try to send a Card or a Hand from the Client to the Server, however, very rarely it works and usually I get a
Exception in thread "main" java.io.StreamCorruptedException: invalid stream header: 434B0005
at java.io.ObjectInputStream.readStreamHeader(Unknown Source)
at java.io.ObjectInputStream.<init>(Unknown Source)
at Hand.deserialize(Hand.java:29)
at KoiKoi_TCP_Server.takeClientTurn(KoiKoi_TCP_Server.java:321)
at KoiKoi_TCP_Server.main(KoiKoi_TCP_Server.java:380)
where Hand.java.29 points at the line
ObjectInputStream o = new ObjectInputStream(b);
in the Hand deserialization method.
I understand that it's telling me that the header is invalid. I'm not sure how to fix it, because it only breaks going one direction and the code is identical. Suggestions?
I'm only sending a solitary object at a time, so I'm not initializing multiple ObjectInputStreams or anything.

I'm not initializing multiple ObjectOutputStreams or anything.
Yes you are. You are initializing a new ObjectOutputStream for every object, and then you're giving yourself the additional problem of knowing how many bytes to read in order to receive each object, and you're getting that wrong, so you're getting out of sync.
Get rid of all this. You don't need it. It is just adding problems. Just use a single ObjectOutputStream and ObjectInputStream, directly, for the life of the socket, constructed directly over the socket streams, and call writeObject() when you want to send an object, and readObject() when you want to read one. Two lines of code. Forget about the byte arrays and the ByteArray/DataInput/OutputStreams altogether.

Serializing/deserializing a SIPDIalog

I was trying to serialize and deserialize a gov.nist.javax.sip.stack.SIPDialog object into Cassandra. But the equals comparison on the deserialized object fails when I compare it with the original SIPDialog object I serialized. SO looks like I am missing something here in serialisation. I am using a ByteArraySerializer to read/write the bytes into Cassandra.
//Saving Dialog
MutationBatch mutationBatch = createMutator();
byte[] dialogBytes = SIPDialogEntity.serializeDialog(dialog);
mutationBatch.withRow(SIPDIALOGS, dialogId)
.putColumn("dialog".getBytes(),dialogBytes,null);
mutationBatch.execute();
public static byte[] serializeDialog(SIPDialog dialog) throws IOException {
ByteArrayOutputStream bStream = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bStream);
oos.writeObject(dialog);
oos.close();
byte[] bytes = bStream.toByteArray();
bStream.close();
return bytes;
}
//Reading Dialog
Column<byte[]> result;
result = getKeySpace().prepareQuery(SIPDIALOGS).getKey(dialogId).getColumn("dialog").execute().getResult();
sipDialog = SIPDialogEntity.deserializeDialog(result.getByteArrayValue());
public static SIPDialog deserializeDialog(byte[] byteArrayDialog) throws IOException, ClassNotFoundException {
System.out.println("DEBUG Reading Dialog Bytes:" + byteArrayDialog );
ByteArrayInputStream bStream = new ByteArrayInputStream(byteArrayDialog);
ObjectInputStream ois = new ObjectInputStream(bStream);
SIPDialog dialog = (SIPDialog) ois.readObject();
ois.close();
bStream.close();
return dialog;
}

The SIPDialog class doesn't override the equals method which is why it fails the comparison. Please open an issue in jain sip at http://java.net/jira/browse/JSIP

hmmmm, If SipDialog is your class, you could just skip all the work and use PlayOrm for cassandra ;). Then you don't need to deal with serializing/deserializing.
If it is not your class, I think I will get them to add a way to add 3rd party beans to be converted to an entity much like Guice does in a binding file so it can bind to an entity that can be saved by PlayOrm. IF you open a ticket on PlayOrm with a request, we could get the feature in probably in as little as 1 week.

How do I Serialize Object to Database for Hibernate to read in Java

I'm currently writing a tool to plug into an existing enterprise application that uses Hibernate. My tool at install time needs to write some values into the database where one of the columns is a serialized version of a setting descriptor object. This object has two lists of objects and a few primitive types.
My current approach is to create a ByteArrayOutputStream and an ObjectOutputStream and then write the ObjectOutputStream to the ByteArrayOutputStream, then passing the resulting byte array into the sql with Spring's 1SimpleJdbcTemplate1. My current issue with this approach is that when the enterprise tool pulls my rows it fails to de-serialze the column with the following:
org.springframework.orm.hibernate3.HibernateSystemException: could not deserialize; nested exception is org.hibernate.type.SerializationException: could not deserialize
I feel I may need to serialize the inner objects, but have no clue how to do that and keep everything together.

Ended up solving my own problem. In the hibernate API there is a class called SerializationHelper that has a static function serialize(Serializable obj) which I was able to use to serialize my object and then insert it into the database. Hibernate was then able to read it in the enterprise app.

You can serealize a Java object into bytes and then store it in a BLOB.
Serialize:
ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
ObjectOutputStream objOut = new ObjectOutputStream(byteOut);
objOut.writeObject(object);
objOut.close();
byteOut.close();
byte[] bytes = byteOut.toByteArray()
Deserialize:
public <T extends Serializable> T getObject(Class<T> type) throws IOException, ClassNotFoundException{
if(bytes == null){
return null;
}
ByteArrayInputStream byteIn = new ByteArrayInputStream(bytes);
ObjectInputStream in = new ObjectInputStream(byteIn);
T obj = (T) in.readObject();
in.close();
return obj;
}

java serialized messages dont contain the correct data in socket-client-server model

hello i have a basic client-server system running using java sockets.
my problem is, that an object that i send from the client to the server does not contain the correct data after it has been sent once.
the first time i send it, it arrives with the correct values, but when i send it another time with different values, it still arrives at the server with the same values as the first time. it also happens if i send a completely different instance of that class. it always arrives with the data, which have been sent the very first time.
when i try this with other objects like java.lang.String it seems to work.
the problematic class looks like this:
public class Vector3f implements Serializable {
private static final long serialVersionUID = 2838034155614698213L;
public float x, y, z;
}
i use objectinputstream and objectoutputstream on both the server and the client to send and receive objects.
let me know, if you need any more information about the system.
thanks!

My guess is that you're changing the values of the fields and then retransmitting the same object. The ObjectOutputStream will notice that it's already sent the original object, and just send a reference the second time.
You could avoid this by calling reset() on the ObjectOutputStream - but I'd be tempted to just use separate instances anyway, possibly even making the class immutable. (Public mutable fields are almost never a good idea.)

The best way in case of serialization you should convert the object into a byte array object and then write into the socket.
// Serialize to a file
ObjectOutput out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
out.writeObject(object);
out.close();
// Serialize to a byte array
ByteArrayOutputStream bos = new ByteArrayOutputStream() ;
out = new ObjectOutputStream(bos) ;
out.writeObject(object);
out.close();
// Get the bytes of the serialized object
byte[] buf = bos.toByteArray();
// Deserialize from a file
File file = new File("filename.ser");
ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
// Deserialize the object
Object obj = (Object) in.readObject();
in.close();
// Get some byte array data
byte[] bytes = getBytesFromFile(file);
// see Reading a File into a Byte Array for the implementation of this method
// Deserialize from a byte array
in = new ObjectInputStream(new ByteArrayInputStream(bytes));
in.close();